The present invention relates to an ink-jet printer for printing an image with ink ejected from a print head and, more particularly, to a head loading device for moving the print head to a print position adjacent to a print medium in the ink-jet printer.
Serial ink-jet printers are conventionally widespread. In this serial ink-jet printer, the carriage is movably attached to a guide bar extending across the paper sheet, and the print head is mounted on this carriage together with a relatively-small-capacity ink cassette. This print head ejects ink supplied from the ink cassette while the carriage moves along the guide bar. Every time the carriage moves across the paper sheet, the paper sheet is fed at a predetermined pitch in a direction perpendicular to the guide bar. Since the print head moves together with the carriage at the time of printing, the print speed and ink supply amount cannot be increased owing to the carriage load and inertia. This ink-jet printer is therefore unsuitable for printing in large quantities at a high speed.
U.S. patent application Ser. No. 09/153,839 filed on Sept. 15, 1998 (now U.S. Pat. No. 6,126,267, issued on Oct. 3, 2000 to Ito et al), discloses a drum rotation type ink-jet printer. This ink-jet printer comprises a rotary drum which rotates in one direction, and a print head for printing an image on a paper sheet held by the rotary drum and rotating together with the rotary drum. The print head has a nozzle unit made up of a plurality of ink-jet nozzles aligned along the shaft of the rotary drum, and prints dots with ink ejected from these ink-jet nozzles. Since the print head does not move at the time of printing, the print speed and ink supply amount can be increased. In this case, ink is supplied to the print head from a large-capacity ink tank arranged in a free space apart from the print head. Thus, the ink-jet printer can print in large quantities at a high speed.
The ink-jet printer must perform a maintenance process for preventing clogging of the ink-jet nozzles or removing bubbles or sheet dust from the ink-jet nozzles periodically, e.g., every three hours. A typical rotary drum type ink-jet printer has a head loading mechanism for moving the print head relatively to the paper sheet. The head loading mechanism sets the print head to a print position where the ink-jet nozzle is apart from the rotary drum by only about 1 mm at the time of printing, and to a maintenance position where the ink-jet nozzle is more apart from the rotary drum than the print position at the time of non-printing. At the time of non-printing, a maintenance unit is inserted between the print head and rotary drum to perform the maintenance process using ink ejected from the ink-jet nozzle.
In the rotary drum type ink-jet printer, the print quality readily degrades due to a positional error generated when the print head returns from the maintenance position to the print position. To prevent this positional error, the head loading mechanism must be assembled at a high precision using high-quality components formed at a high precision. This inhibits the manufacture of a low-cost ink-jet printer. Even if the print head has been accurately set to the print position by the head loading mechanism, when the distance between the ink-jet nozzle and rotary drum fluctuates due to vibrations caused by the rotation of the motor or the like, the print quality degrades.
It is an object of the present invention to provide a head loading device capable of accurately and stably setting the print head at the print position while reducing the manufacturing cost.
According to the present invention, there is provided a head loading device which comprises a print head for ejecting ink from a print position adjacent to a print medium to print an image with the ink, an elevator for moving the print head upward from the print position at the time of non-printing and downward to the print position at the time of printing, and a support mechanism for supporting, at least three points, the print head moved to the print position by the elevator to hold the print head at a preset distance from the print medium.
In this head loading device, the print head can be reliably supported by the support member instead of the elevator, when the print head has been moved to the print position after a maintenance process is performed at a position above the print position. The print head can be accurately and stably set at the print position without requiring high reliability of the elevator, which increases the manufacturing cost.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.